Lawn mower

ABSTRACT

A lawn mower comprises a power source for rotatably driving an output shaft, a housing having an interior space having a generally spiral-shaped portion, and a cutting blade disposed in the interior space of the housing and connected to the output shaft for rotation therewith to cut grass. The rotating cutting blade coacts with the spiral-shaped portion of the interior space to generate a swirling air flow that causes the cut grass to swirl within the interior space. A grass discharge passage communicates with the interior space of the housing and discharges therethrough grass cut by the cutting blade and swirling within the interior space of the housing. A pivotal shutter is pivoted about a generally vertical axis by manual operation of a control member to open and close the grass discharge passage. The pivotal shutter comprises a pivotal shaft and a unitary shutter member mounted on the pivotal shaft to undergo pivotal movement therewith for opening and closing the grass discharge passage.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of prior U.S. application Ser. No. 10/378,755, filed Mar. 4, 2003 and now U.S. Pat. No. 6,862,875, which is hereby incorporated by reference, and priority thereto for common subject matter is hereby claimed.

BACKGROUND OF THE INVENTION

(1) Field of the Invention

The present invention relates to lawn mowers, and more particularly, to rotary lawn mowers for cutting grass by rotating cutting blades housed in housings which open downward toward the grass.

(2) Background Information

This kind of rotary lawn mower includes (1) lawn mowers of a type for use in a so-called bagging mode for receiving grass cut by cutting blades in grass receptacles such as bags and (2) lawn mowers of a type for use in a so-called mulching mode for cutting grass cut by cutting blades more finely within housings and discharging the cut grass downward of the housings. The lawn mowers of type (1) can remove all cut grass clippings, providing a good finish of the cut grass, and are thus commonly used in golf courses or the like. The lawn mowers of type (2) can eliminate the need for dumping grass clippings by returning the grass clippings to the lawns, and are thus commonly used in parks or the like.

It is, however, inconvenient to selectively use the two types of lawn mowers for their respective suitable uses. In recent years, an art of allowing a single lawn mower to serve as both types (1) and (2) has been developed (e.g., Japanese Patent Laid-Open Publication No. SHO-64-3441 and U.S. Pat. No. 4,951,449).

SHO-64-3441 discloses that a grass discharge chute can be mounted on a top plate of a housing to set it as a bagging-mode housing. With this structure, a bag is attached to an outlet of the grass discharge chute so that grass cut by a cutting blade can be received in the bag (bagging mode).

The lawn mower of SHO-64-3441 can also remove the grass discharge chute and mount a cover plate on the top plate of the housing to switch it into a mulching-mode housing. With this structure, grass cut by the cutting blade can be discharged downward of the housing (mulching mode).

A lawn mower of U.S. Pat. No. 4,951,449 has a bagging-mode housing with a grass discharge chute extended rearward and upward from its top plate. The bagging-mode housing has a scroll portion for allowing grass cut by a cutting blade to swirl within the housing while directing it to the grass discharge chute. A chute plug blocking the grass discharge chute can be removed to attach a bag to the grass discharge chute, thereby to receive grass cut by the cutting blade in the bag (bagging mode).

The lawn mower of U.S. Pat. No. 4,951,449 can also block the grass discharge chute with the chute plug to discharge grass cut by the cutting blade downward of the bagging-mode housing (mulching mode).

The lawn mower of SHO-64-3441 is switched between the bagging-mode housing and the mulching-mode housing by manually changing parts. The mode switching every time requires manual change of parts, inefficiently involving time-consuming and troublesome parts-changing work.

The lawn mower of U.S. Pat. No. 4,951,449 can switch the bagging-mode housing between the bagging mode and the mulching mode only by mounting or demounting the chute plug to or from the grass discharge chute. The mode switching operation is thus relatively easy.

However, the bagging-mode housing is also used in the mulching mode without change. The bagging-mode housing has, as described above, a scroll portion for allowing grass clippings cut by the cutting blade to swirl within the housing while directing the grass clippings to the grass discharge chute.

In the mulching mode, grass clippings are cut more finely by the cutting blade while being caused to swirl within the housing, and the swirling grass clippings are discharged downward of the housing. The cross-sectional area of the housing is larger at a portion where the scroll portion lies and smaller at a portion without the scroll portion. The flow velocity of an air flow swirling grass clippings within the housing, that is, a swirling flow, can thus be largely changed between the portion with the scroll portion and the portion without the scroll portion. The rapid change of the flow velocity of the swirling flow can be a factor in the retention of grass clippings within the housing.

If the flow velocity is rapidly reduced near the rear end of the scroll portion, for example, grass clippings accumulate on the inner surface of the housing at that portion, or grass clippings accumulate at the inlet of the grass discharge chute. A certain amount of accumulation within the housing reduces the flow of a swirling flow. Suspending the grass cutting operation each time it occurs and removing accumulated grass clippings prevents continuous mowing operations. The resulting operating inefficiency leaves room for improvement.

Furthermore, partial accumulation of grass clippings within the housing prevents grass clippings from being evenly discharged downward from the housing. The return amount of grass clippings returned from the housing to the lawn is thus nonuniform, resulting in a reduced finished quality of the grass cutting.

Thus, desired is a lawn mower which increases operating efficiency in a mulching mode while securing operating efficiency in a bagging mode, thereby improving the finished quality of grass cutting.

SUMMARY OF THE INVENTION

According to the present invention, there is provided a lawn mower, which comprises a power source with an output shaft extending downward, a housing provided below the power source and opening downward, a cutting blade housed in the housing and attached to the output shaft, a grass discharge passage extending rearward and upward from the housing, a member provided in the grass discharge passage for opening and blocking the passage, a grass receptacle removably mounted to an outlet of the grass discharge passage, a scroll portion provided in the housing for allowing grass cut by the cutting blade to swirl within the housing while guiding it to the grass discharge passage, and a guide provided along the scroll portion beneath a top plate of the housing. When the grass discharge passage is opened, grass cut by the cutting blade is received through the grass discharge passage in the grass receptacle; when the grass discharge passage is blocked, grass cut by the cutting blade is discharged downward of the housing.

Specifically, in the present invention, the guide is placed along the scroll portion for allowing grass clippings to swirl within the bagging-mode housing while directing them toward the grass discharge passage, the guide being provided beneath the top plate of the housing, and a rear guide end of the guide is opposed to the passage opening facing the housing of the grass discharge passage, so that the direction of an air flow swirling grass clippings within the housing, that is, a swirling flow of air and entrained grass clippings, can be gradually changed and guided toward the passage opening by the guide.

Furthermore, since the guide placed along the scroll is provided beneath the top plate of the bagging-mode housing, the cross-sectional area of the housing can be gradually changed between a portion with the scroll portion and a portion without the scroll portion. The gradual change of the cross-sectional area results in a gradual change of the flow velocity of the swirling flow between the portion with the scroll portion and the portion without the scroll portion. Thus in the mulching mode in which the grass discharge passage is blocked off, a swirling flow guided by the guide smoothly continues swirling within the housing. Grass clippings thus hardly accumulate within the housing. No accumulation of grass clippings allows continuous grass cutting operations. This results in an increased efficiency in mulching-mode operations. Further, grass clippings can be discharged evenly downward from the housing. The return amount of grass clippings returned from the housing to the lawn is thus uniform, improving the finished quality of the grass cutting.

In the bagging mode in which the grass discharge passage is opened, a swirling flow of air and entrained grass clippings (carrying flow) guided by the guide flows from the passage opening into the grass discharge passage to discharge grass clippings into the grass receptacle. The operating efficiency in the bagging mode can be secured.

In this manner, the operating efficiency in the mulching mode can be improved with the operating efficiency in the bagging mode being secured, thus improving the finished quality of grass cutting.

The rear guide end of the guide is preferably generally oriented toward the bottom of the passage opening. Thus generally orienting the rear guide end of the guide toward the bottom of the passage opening allows the flow direction of a swirling flow to be gradually changed and guided below the passage opening. The cross-sectional area of the housing can thus be more gradually changed between the portion with the scroll portion and the portion without the scroll portion. The more gradual change in the cross-sectional area results in a more gradual change in the flow velocity of the swirling flow between the portion with the scroll portion and the portion without the scroll portion. As a result, in the mulching mode, the swirling flow guided by the guide more smoothly continues swirling within the housing. Local accumulation of grass clippings within the housing can thus be further prevented. More continuous grass cutting operations can thus be performed, further increasing operating efficiency in the mulching mode. Also the return mount of grass clippings returned from the housing to the lawn can be more evenly distributed, further improving the finished quality of the grass cutting.

The member for opening and blocking the grass discharge passage may be a plug member that can be removed out of or inserted into the grass discharge passage. The plug member extends toward the rear guide end of the guide within the housing, with the bottom of the plug member being placed at a height substantially identical to that of the rear guide end. Only removing or inserting the plug member out of or into the grass discharge passage allows the bagging-mode housing to be switched between the bagging mode and the mulching mode. The mode switching operation is easy and allows short-time switching. The lower end of the plug member that extends toward the rear guide end of the guide is placed at a height substantially identical to that of the rear guide end, so that a swirling flow guided by the guide passes below the plug member in the mulching mode with the grass discharge passage blocked by the plug member.

In this manner, a swirling flow guided by the guide can be further gradually changed and guided toward the portion without the scroll portion by the lower end of the plug member. The cross-sectional area of the housing can thus be more gradually changed between the portion with the scroll portion and the portion without the scroll portion. The more gradual change in cross-sectional area results in a more gradual change in the flow velocity of the swirling flow between the portion with the scroll portion and the portion without the scroll portion. As a result, in the mulching mode, a swirling flow guided by the guide more smoothly continues swirling within the housing. Grass clippings can thus be further prevented from locally accumulating within the housing.

The member for opening and blocking the grass discharge passage may be a shutter provided to selectively open and close the grass discharge passage. The shutter comprises a pivotal shaft extending generally vertically and located, for example, in the vicinity of the passage opening, adjacent one of left and right vertical walls of the grass discharge passage, a vertical shield in the form of a vertical plate attached at a swing proximal end thereof to the pivotal shaft for opening and closing the passage opening by a pivoting or swinging operation, and a horizontal shield in the form of a horizontal plate extending from the bottom of the vertical shield toward the outlet for blocking a lower portion of the passage opening. A control member is coupled to the pivotal shaft and is manually operable to adjust the degree of opening of the passage opening via the vertical shield and the horizontal shield. The degree of opening of the passage opening can thus be desirably and easily adjusted by the shutter. That is, the simple control of the shutter opening allows switching between the bagging mode in which the shutter is fully opened to receive grass clippings in the grass receptacle, the mulching mode in which the shutter is fully closed to discharge grass clippings downward of the housing, and an intermediate mode between the bagging mode and the mulching mode in which the shutter is opened to a desired degree. There is no need to change parts every time the mode is switched. Further, opening the shutter to a desired degree allows minute and preferable setting of the form of discharge of grass clippings according to lawn conditions, required finished quality, or preference.

The rear guide end of the guide is preferably placed at a higher level than the bottom of the passage opening. The rear guide end is preferably formed in a wave shape.

Lawn mowers for use in a bagging mode generally cause grass cut by cutting blades to swirl within housings while guiding the cut grass to grass discharge passages. The shape of the bagging-mode housings is thus generally spiral. On the other hand, lawn mowers for use in a mulching mode cut grass cut by cutting blades more finely by the cutting blades within housings. The shape of the mulching-mode housings is thus generally uniform in cross-sectional shape. The shape of the housings for use in a bagging mode is thus different from the shape of the housings for use in a mulching mode.

The lawn mower of the present invention uses a single housing to operate in the bagging mode, mulching mode and intermediate mode, the scroll portion being provided in the housing for efficiently performing bagging-mode operations. The guide is placed along the scroll portion, which is provided beneath the top plate of the housing, and the rear guide end of the guide is opposed to the passage opening, for efficiently performing mulching-mode operations.

When the shutter is opened, the scroll portion and the guide allow grass clippings to swirl while smoothly guiding them to the passage opening. When the shutter is closed, the guide guides grass clippings swirling in the scroll portion for smooth flow along the closed shutter. The same applies to the intermediate mode. With the single housing, operations in the bagging mode, mulching mode and intermediate mode can thus be more efficiently performed.

In the present invention, as described above, the height of the rear guide end of the guide is set greater than that of the bottom of the passage opening. Thus in the intermediate mode, grass clippings swirling along the guide can be easily taken into the grass discharge passage. As a result, a desired amount of grass clippings can be securely received through the grass discharge passage in the grass receptacle. The ratio between the amount of glass clippings to be received in the grass receptacle and the amount of grass clippings to be discharged downward of the housing can thus be relatively precisely set in the intermediate mode, thereby improving workability in the intermediate mode.

When the cutting blade is rotated, an air flow (swirling flow) along the guide is produced below the guide. This flow tends to become a vortex flow at the rear guide end. When the vortex flow is excessive, grass clippings are likely to be drawn into the vortex flow. As a result, in the bagging mode or the intermediate mode, the grass clippings have difficulty in flowing into the passage opening.

In the present invention, as described above, the rear guide end of the guide has a wave shape having alternating depressions and projections. Thus air flows at depressions in the wave shape interfere with air flows at projections in the wave shape to reduce the generation of vortex flows, resulting in a straightened air flow flowing into the passage opening. As a result, in the bagging mode or the intermediate mode, grass clippings easily flow into the passage opening. Grass clippings are thus allowed to smoothly flow into the grass receptacle through the grass discharge passage to be more securely received.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the present invention will be described in detail below, by way of example only, with reference to the accompanying drawings, in which:

FIG. 1 is a perspective view of a lawn mower according to a first embodiment of the present invention;

FIG. 2 is a left side view of the lawn mower shown in FIG. 1;

FIG. 3 is an enlarged plan view of the lawn mower shown in FIG. 2;

FIG. 4 is an enlarged bottom view of the lawn mower shown in FIG. 2;

FIG. 5 is a cross-sectional view taken along line 5-5 in FIG. 4;

FIG. 6 is a cross-sectional view taken along line 6-6 in FIG. 4;

FIG. 7A is a perspective view of a rear guide end of a guide shown in FIG. 4; and FIG. 7B is a cross-sectional view illustrating the relationship of the rear guide end with a housing;

FIG. 8 is an enlarged cross-sectional view taken along line 8-8 in FIG. 3;

FIG. 9 is a perspective view of the housing, an opening control lever and surrounding parts according to the first embodiment;

FIG. 10 is a cross-sectional view illustrating the relationship among the housing, a cutting blade, a passage opening of a grass discharge passage and a shutter according to the present invention, the passage opening being closed by a shutter member;

FIG. 11 is a cross-sectional view illustrating the shutter member put in an intermediate mode from the state in FIG. 10;

FIG. 12 is a cross-sectional view of the shutter member brought into a fully-opened state from the state shown in FIG. 11;

FIG. 13 is a perspective view illustrating the shutter in a fully-closed state;

FIG. 14 is a perspective view illustrating the shutter in a half-opened state;

FIG. 15 is a perspective view illustrating the shutter in the fully-opened state;

FIG. 16 is a left side view of a lawn mower according to a second embodiment of the present invention;

FIG. 17 is a plan view of the lawn mower shown in FIG. 16;

FIG. 18 is a bottom view of the lawn mower shown in FIG. 16;

FIG. 19 is a cross-sectional view taken along line 19-19 in FIG. 18;

FIG. 20 is a cross-sectional view taken along line 20-20 in FIG. 19;

FIG. 21 is a perspective view of a plug member according to the second embodiment of the present invention; and

FIG. 22 is a cross-sectional view corresponding to FIG. 19, illustrating a state in a bagging mode in which a grass discharge passage is opened.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Initial reference is made to FIGS. 1 to 15 illustrating a first embodiment of a lawn mower of the present invention.

In FIG. 1, a lawn mower 10 of this embodiment has a housing 11 serving as a body of the lawn mower, left and right front wheels 12, 12 provided at the front of the housing 11, and left and right rear wheels 13, 13 as driving wheels provided at the rear of the housing 11 (only the left ones of the left and right ones are shown in the figure.). The lawn mower 10 further has a single grass cutting blade 14 provided in a central portion within the housing 11, an engine 15 provided on the top of the housing 11 for driving the rear wheels 13, 13 and the cutting blade 14, and a continuously variable transmission (not shown) interposed between the engine 15 and the rear wheels 13, 13 within the rear of the housing 11. An operating handle 16 extends rearward from the housing 11. The lawn mower 10 is a walk-behind self-propelled working machine.

As shown in FIG. 2, an output shaft 15 a extends downward from the engine 15 as a power source. Below the engine 15 is provided the housing 11 opening downward. The cutting blade 14 housed in the housing 11 is attached to the output shaft 15 a. A grass discharge passage 21 with a substantially rectangular cross section extends from the housing 11 rearward and upward. At an outlet of the grass discharge passage 21 is provided a receptacle mounted portion 22. A grass receptacle 23 such as a grass bag is removably mounted to the receptacle mounted portion 22 (that is, to the outlet of the grass discharge passage 21) so as to receive grass cut by the cutting blade 14 (hereinafter referred to as “grass clippings”) through the grass discharge passage 21 in the grass receptacle 23.

A receptacle cover 31 is attached to a rear upper portion of the housing 11 in an upwardly and downwardly swingable manner. A cutting blade clutch lever 32, a drive clutch lever 33 and a speed change lever 34 are provided on the operating handle 16.

As shown in FIG. 3, the cutting blade 14 rotates in a clockwise direction as shown by an arrow Ra to cut grass and also to produce an air flow as shown by a hollow arrow Rb, that is, a swirling flow (carrying flow) within the housing 11, transporting grass clippings into the grass receptacle 23. The lawn mower 10 is self-propelled in a forward direction to proceed with the grass cutting operation.

As shown in FIG. 4, the lawn mower 10 of this embodiment is characterized in that a shutter 40 is provided in the vicinity of a passage opening 24 facing the housing 11 of the grass discharge passage 21 so that the degree of opening of the passage opening 24 is adjusted with the shutter 40. That is, the shutter 40 is a member for opening and closing (blocking) the grass discharge passage 21.

The housing 11 is in the form of a spiral case or scroll case with a scroll portion 11 d, that is, a bagging-mode housing for allowing grass clippings to swirl within the housing while directing them to the grass discharge passage 21 as shown by the hollow arrow Rb.

More specifically, the housing 11 has an outer tubular portion 11 b and an inner tubular portion 11 c with a diameter smaller than that of the outer tubular portion 11 b, which are cylindrical in shape and disposed concentrically with the shaft center SC of the output shaft 15 a. The grass discharge passage 21 extends rearward from the outer tubular portion 11 b, tangentially to the outer tubular portion 11 b. The scroll portion 11 d is a space enclosed by a top plate 11 a, the outer tubular portion 11 b and the inner tubular portion 11 c, and the scroll portion 11 d communicates with the passage opening 24 facing the housing 11 of the grass discharge passage 21.

The housing 11 allows glass clippings to sufficiently swirl with a swirling flow within the housing 11, as shown by hollow arrows Rc, to provide an efficient mulching-mode operation. More specifically, a guide 70 is placed along the scroll portion 11 d beneath the top plate 11 a of the housing 11 (see FIG. 5), and a rear guide end 71 of the guide 70 is oriented to face (that is, opposed to) the passage opening 24. The guide 70 has a front guide portion 72, and a scroll plate 81 is disposed adjacent to the rear guide end 71 of the guide 70. As is also apparent from FIG. 4, the lawn mower 10 allows the guide 70 and the scroll plate 81 to be disposed along the scroll portion 11 d in slightly spaced-apart relation on the opposite sides of the passage opening 24.

The height of the guide 70 and the scroll plate 81 within the scroll portion 11 d is substantially the same. Changes in the cross section of the scroll portion 11 d (i.e., changes in the cross-sectional shape and dimension) are thus relatively small despite connection of the grass discharge passage 21 to the housing 11. As a result, the scroll portion 11 d allows smooth and sufficient swirling of air and grass clippings.

As shown in FIG. 5, the grass discharge passage 21 extends rearward and upward from the housing 11 in the location of the scroll portion 11 d, and the receptacle mounted portion 22 is provided at the outlet of the grass discharge passage 21. More specifically, the grass discharge passage 21 has a substantially rectangular cross section and is formed by an enclosure having a top plate 21 a extended rearward and upward from a middle portion of the top plate 11 a of the housing 11, a bottom plate 21 b extended rearward and upward from a middle height of the outer tubular portion 11 b of the housing 11, and left and right side plates 21 c, 21 c between the top plate 21 a and the bottom plate 21 b (only the right side plate 21 c is shown in this figure). Reference numeral 21 e denotes a proximal end portion of the top plate 12 a relative to the top plate 11 a.

The passage opening 24 of the grass discharge passage 21 faces the housing 11 and is enclosed by a proximal end portion of the top plate 21 a, a proximal end portion of the bottom plate 21 b and proximal end portions of the left and right side plates (left and right vertical walls) 21 c, 21 c, relative to the housing 11.

As is clear from the above, since the bottom plate 21 b is absent at a portion of the passage opening 24 of the grass discharge passage 21, the portion has a downwardly-opening channel-shaped cross section (a substantially U-shaped cross section opening downward) instead of the substantially rectangular cross section. The bottom of the passage opening 24, that is, a proximal end 21 d of the bottom plate 21 b relative to the outer tubular portion 11 b, is lower in level than the top plate 11 a of the housing 11 as is obvious.

In the mulching mode, the lawn mower 10 causes grass cut by the cutting blade 14 (see FIG. 4) to swirl upward within the scroll portion 11 d, cutting more finely the grass clippings falling after reaching near the top plate 21 a with the cutting blade 14, and discharging them downward of the housing 11.

In the bagging mode and the intermediate mode, the lawn mower 10 also causes grass clippings to swirl upward within the scroll portion 11 d as will be understood. The above-described configuration of a portion of the passage opening 24 of the grass discharge passage 21 facilitates the entering of swirling grass clippings from the passage opening 24 into the grass discharge passage 21 as shown by arrows in the bagging mode or the intermediate mode with the shutter 40 opened.

FIG. 5 further illustrates that the guide 70 is provided below the top plate 11 a with a certain clearance within the scroll portion 11 d, and the height of the rear guide end 71 of the guide 70 is set larger by a height H1 than that of the bottom of the passage opening 24. As shown in FIG. 6, the guide 70 is secured to the housing 11 with a plurality of bolts 75.

The height of the rear guide end 71 of the guide 70 for directing grass clippings toward the grass discharge passage 21 set larger than that of the bottom of the passage opening 24 facilitates taking grass clippings swirling along the guide 70 into the grass discharge passage 21 in the intermediate mode. As a result, a desired amount of grass clippings can be securely received through the grass discharge passage 21 in the grass receptacle 23 (see FIG. 1). The ratio between the amount of grass clippings to be received in the grass receptacle 23 and the amount of grass clippings to be discharged downward of the housing 11 can thus be relatively precisely set in the intermediate mode, thereby improving the workability in the intermediate mode.

Now, with reference to FIGS. 4 and 5, the configuration of the housing 11 will be summarized.

The housing 11 has the scroll portion 11 d in a scroll shape connected to the passage opening 24 of the grass discharge passage 21 extending rearward and upward. The top plate 11 a is thus gradually higher in level in a spiraling direction of the scroll portion 11 d (in the direction of the hollow arrows Rc in FIG. 4), that is, formed deeper rearward of the plane of the paper of FIG. 4. In other words, as shown in FIG. 4, the height of the top plate 11 a at the scroll portion 11 d is smallest at a portion where the scroll plate 81 is provided, becomes progressively larger in the direction of the hollow arrows Rc, and is largest at a portion connected to the passage opening 24.

In this embodiment, a portion of the scroll portion 11 d provided with the scroll plate 81 is referred to as a “portion without the scroll portion” and the remaining portion without the scroll plate 81 is referred to as a “portion with the scroll portion.”

In this embodiment, the guide 70 is placed along the scroll portion 11 d for allowing grass clippings to swirl within the bagging-mode housing 11 while directing them toward the grass discharge passage 21, the guide 70 is provided beneath the top plate 11 a of the housing 11, and the rear guide end 71 of the guide 70 is opposed to the passage opening 24, so that the flow direction Rc (the direction of the hollow arrows Rc) of an air flow that swirls the grass clippings within the housing 11, that is, a swirling flow, can be gradually changed and guided toward the passage opening 24 with the guide 70.

Furthermore, since the guide 70 placed along the scroll portion 11 d is provided beneath the top plate 11 a of the bagging-mode housing 11, the cross-sectional area of the housing 11 can be gradually changed between a portion with the scroll portion 11 d and a portion without the scroll portion 11 d. The gradual change of the cross-sectional area results in a gradual change of the flow velocity of the swirling flow between a portion with the scroll portion 11 d and a portion without the scroll portion 11 d.

Thus, in the mulching mode in which the grass discharge passage 21 is closed or blocked off, a swirling flow guided with the guide 70 smoothly continues swirling within the housing 11. Grass clippings thus hardly accumulate within the housing 11. The absence of accumulation of grass clippings allows continuous grass cutting operations. This results in an increased efficiency in mulching-mode operations. Further, grass clippings can be evenly discharged downward from the housing 11. The return amount of grass clippings returned from the housing 11 to the lawn is thus uniform, improving the finished quality of the grass cutting.

In the bagging mode with the grass discharge passage 21 opened, a swirling flow (carrying flow) guided by the guide 70 flows from the passage opening 24 into the grass discharge passage 21 to discharge grass clippings into the grass receptacle 23. The operating efficiency in the bagging mode can be secured.

In this manner, the operating efficiency in the mulching mode can be improved with the operating efficiency in the bagging mode being secured, thus improving the finished quality of grass cutting.

FIGS. 7A and 7B are structural diagrams of the rear guide end 71 of the guide 70 and surroundings; FIG. 7A is a perspective view of the rear guide end 71 of the guide 70, taken from below; and FIG. 7B is a cross-sectional view of the relationship of the rear guide end 71 with the housing 11, taken from the side. FIG. 7A illustrates that the rear guide end 71 of the guide 70 which is formed of a flat plate has a plurality of depressions 71 a and a plurality of projections 71 b which are alternately arranged across the plate in a wave shape.

When the cutting blade 14 (see FIG. 4) is rotated, an air flow is generally produced along the guide 70 below the guide 70. This flow tends to become a vortex flow at the rear guide end 71. When the vortex flow is excessive, grass clippings are likely to be drawn into the vortex flow. As a result, in the bagging mode or the intermediate mode, the grass clippings have difficulty in flowing into the passage opening 24 (see FIG. 4).

In the present embodiment, the wave-shaped rear guide end 71 of the guide 70 causes interference between air flows W1 at the depressions 71 a in the wave shape and air flows W2 at the projections 71 b to reduce the generation of vortex flows, straightening the air flow flowing into the passage opening 24. As a result, in the bagging mode or the intermediate mode, grass clippings more easily flow into the passage opening 24. Grass clippings are thus allowed to smoothly flow into the grass receptacle 23 (see FIG. 1) through the grass discharge passage 21 (see FIG. 4) to be more securely received.

FIG. 8 is a cross-sectional view taken along line 8-8 in FIG. 3. The shutter 40 includes a generally vertically-extending pivotal shaft 44 provided in the vicinity of the passage opening 24, adjacent either of the left and right side plates 21 c of the grass discharge passage 21, that is, either of the left and right vertical walls 21 c, a vertical shield 45 attached at its swing proximal end to the pivotal shaft 44 for opening and closing the passage opening 24 by a swinging or pivoting operation, and a horizontal shield 46 extending from the bottom of the vertical shield 45 toward the receptacle mounted portion 22 (see FIG. 5) for blocking a lower portion of the passage opening 24. A manually movable control member 53 is coupled to the pivotal shaft 44 for pivoting the pivotal shaft 44 in response to manual movement of the control member 53 to effect pivotal movement of the shutter 40 for opening and closing the grass discharge passage 21. In this embodiment, the control member 53 comprises a lever extending sideways of the lawn mower 10 for easy access by the operator.

The shutter 40 has a lower bearing 42 attached to a lower portion of the left side plate 21 c of the grass discharge passage 21 with a support bracket 41, and an upper bearing 43 attached to the top plate 21 a of the grass discharge passage 21. The upper and lower bearings 42 and 43 pivotably support the pivotal shaft 44. The vertical shield 45 and the horizontal shield 46 are attached to the pivotal shaft 44. Also apparent from the figure, the grass discharge passage 21 and the shutter 40 are at a higher level than the cutting blade 14. In this manner, the cutting blade 14, even when rotating, does not interfere with the grass discharge passage 21 and the shutter 40.

The pivotal shaft 44 is connected at its upper end to the control member 53, and the control member 53 is resiliently biased with a return spring 54 such as a torsion spring to a neutral position (defined by a location notch 56 b) shown by solid lines. The vertical shield 45 and the horizontal shield 46 are formed by bending a single piece of plate material in a substantially L shape (in a side view), forming an integrally-formed unitary shutter member 47. As shown in FIG. 5, the pivotal shaft 44 is pivotal about a generally vertical axis A, which in this embodiment is inclined forwardly at an angle θ=8° from the normal. The pivotal shaft 44 is pivoted in opening and closing directions by manual manipulation of the control member 53 to correspondingly pivot or swing the shutter member 47 about the generally vertical axis A.

FIG. 9 is a perspective view of the housing, the control member and surrounding parts according to the present embodiment, illustrating that a control guide 56 is provided on a rear upper surface of the housing 11 and the control guide 56 guides the movement of the control member 53. The control guide 56 has a horizontally-elongated guiding long hole 56 a which receives the control member 53 therethrough and a plurality of vertically-elongated location notches 56 b arranged along the guiding long hole 56 a. The location notches 56 b each extend downward from the guiding long hole 56 a. Reference numeral 55 denotes a grip.

FIG. 10 is a plan view illustrating the relationship among the housing, the cutting blade, the passage opening of the grass discharge passage and the shutter according to the present invention, illustrating that the shutter member 47 provided in the grass discharge passage 21 allows the passage opening 24 to be opened and closed. As is clear from the figure, the proximal end of the right side plate 21 c of the grass discharge passage 21 is tangential to the outer tubular portion 11 b, and the proximal end of the left side plate 21 c is tangential to the inner tubular portion 11 c.

As described above, the passage opening 24 of the grass discharge passage 21 is enclosed by the proximal end 21 e of the top plate 21 a (see FIG. 5), the proximal end portion of the bottom plate 21 b and the proximal end portions of the left and right side plates 21 c, 21 c, relative to the housing 11, the passage opening 24 being an opening portion in a substantially crescent shape in a plan view. At the opening portion, the pivotal shaft 44 and the vertical shield 45 are disposed as shown in FIG. 10. This arrangement allows a more smooth flow of grass clippings in the bagging mode in which the vertical shield 45 is fully opened or in the intermediate mode in which the vertical shield 45 is half opened.

In the mulching mode in which the vertical shield 45 is fully closed, however, the grass discharge passage 21 communicates with the scroll portion 11 d via the passage opening 24. This reduces by half the effect of closing the vertical shield 45. To prevent this there is provided the horizontal shield 46 extending from the bottom of the vertical shield 45 toward the receptacle mounted portion 22 for closing a lower portion of the passage opening 24. This results in an increased shielding efficiency in shielding the grass discharge passage 21 against the scroll portion 11 d with the vertical shield 45 fully closed. In this manner, operations in the bagging mode, mulching mode and intermediate mode can be more efficiently performed with the single housing 11.

The control guide 56 is a member serving as a guide for the control member 53 when the degree of opening of the shutter 40 is controlled, having, e.g., five location notches 56 b. The location of the location notch 56 b facing one end of the guiding long hole 56 a defines a full-close position and the location of the location notch 56 b facing the other end of the guiding long hole 56 a defines a full-open position. The spacing between adjacent location notches 56 b may, for example, be set to correspond to progressive opening of the shutter 40 in 25% increments.

Now, the operation of the lawn mower 10 of the above structure will be described with reference to FIGS. 10 to 15.

FIG. 10 illustrates that the control member 53 is put in the full-close position to put the shutter member 47 in a full-close position (0% opening) to close the grass discharge passage 21. Closing the passage opening 24 with the shutter member 47 allows the lawn mower 10 to be set in a condition for use in the mulching mode. A portion of the passage opening 24 is closed by the horizontal shield 46. In this state, grass clippings swirl below the passage opening 24 in a direction of arrows within the housing 11, that is, within the scroll portion 11 d. As a result, the grass clippings can be cut more finely by the cutting blade 14 within the housing 11 and discharged downward of the housing 11. From this state, the shutter member 47 can be swung clockwise in the figure to be opened.

FIG. 11 illustrates that the control member 53 is put in a half-open position to put the shutter member 47 in a half-open position (50% opening) in which the shutter member 47 projects into the grass discharge passage 21 to partly close the grass discharge passage 21. Opening the passage opening 24 by a desired degree of opening with the shutter member 47 allows the lawn mower 10 to be set in a condition for use in the intermediate mode (mode intermediate between the bagging mode and the mulching mode), returning part of grass cut by the cutting blade 14 to the ground and receiving the rest in the grass receptacle 23 (see FIG. 1). Also in this mode, a portion of the passage opening 24 is closed by the horizontal shield 46.

FIG. 12 illustrates that the control member 53 is put in a full-open position to put the shutter member 47 in a full-open position (100% opening) in which the shutter member 47 projects into the grass discharge passage 21 to open the grass discharge passage 21. With the shutter member 47 put in the full-open position, the vertical shield 45 is adjacent an inner surface of the left side plate 21 c. Full opening of the passage opening 24 allows the lawn mower 10 to be set in a condition for use in the bagging mode and receiving grass cut by the cutting blade 14 in the grass receptacle 23 (see FIG. 1).

In this manner, the shutter 40 is provided at the passage opening 24 facing the housing 11 of the grass discharge passage 21 extending rearward from the downward-opening housing 11. The shutter 40 comprises, in this embodiment, the generally vertically-extending pivotal shaft 44 provided in the vicinity of the passage opening 24, adjacent either of the left and right vertical walls 21 c of the grass discharge passage 21, the vertical shield 45 attached at its swing proximal end to the pivotal shaft 44 for opening and closing the passage opening 24 by a swinging or pivoting operation, and the horizontal shield 46 extending from the bottom of the vertical shield 45 toward the receptacle mounted portion 22 for closing the lower portion of the passage opening 24. The control member 53 is coupled to the pivotal shaft 44 for pivoting the pivotal shaft 44 so that the degree of opening of the passage opening 24 can be desirably adjusted with the shutter 40.

Only controlling the opening of the shutter 40 with a simple configuration allows switching between the bagging mode in which the shutter 40 is fully opened to receive grass clippings in the grass receptacle 23 (see FIG. 1), the mulching mode in which the shutter 40 is fully closed to discharge grass clippings downward of the housing 11, and the intermediate mode between the bagging mode and the mulching mode in which the shutter 40 is opened to a desired degree. By such a construction, there is no need to change parts every time the mode is switched, and the grass receptacle 23 can be detached from and attached to the discharge end portion of the grass discharge passage 21 independently of pivotal movement of the shutter 40 between the fully opened and closed positions.

Further, opening the shutter 40 to a desired degree allows minute and preferable setting of the form of discharge of grass clippings, according to lawn conditions, required finished quality, or preference. Furthermore, switching to the intermediate mode allows a reduction of the discharged flow amount of grass clippings discharged from the housing 11 to the grass receptacle 23. This lengthens the time during which grass clippings accumulate in the grass receptacle 23, thereby reducing the frequency of having to empty the grass receptacle 23. For efficient operations in the bagging mode, the scroll portion 11 d is provided in the housing 11 for allowing grass clippings to swirl within the housing 11 while directing them to the grass discharge passage 21. Also for efficient operations in the mulching mode, the guide 70 is placed along the scroll portion 11 d, being provided beneath the top plate 11 a of the housing 11, and the rear guide end 71 of the guide 70 is opposed to the passage opening 24.

Thus, when the shutter is opened as shown in FIG. 12, the scroll portion 11 d and the guide 70 (see FIG. 5) allow grass clippings to swirl within the scroll portion 11 d while being smoothly guided to the passage opening 24.

When the shutter 40 is closed as shown in FIG. 10, grass clippings swirling in the scroll portion 11 d can be guided by the guide plate 70 (see FIG. 5) to smoothly flow along the shutter 40 in the closed state. The same is true in the intermediate mode.

In this manner, operations in the bagging mode, mulching mode and intermediate mode can be more efficiently performed with the single housing 11.

The housing 11 has, as described above, the outer tubular portion 11 b and the inner tubular portion 11 c which are cylindrical about the shaft center SC (see FIG. 4). The grass discharge passage 21 extends tangentially to the outer tubular portion 11 b. The shutter 40 is provided at the passage opening 24 facing the housing 11. The direction of the grass discharge passage 21 extending from the outer tubular portion 11 b agrees with the rotation direction Ra of the cutting blade 14. In other words, the grass discharge passage 21 extends tangentially to the rotating path of the cutting blade 14.

The passage opening 24 opens in the rotation direction Ra of the cutting blade 14. The outer side plate 21 c of the grass discharge passage 21 extends tangentially to the outer tubular portion 11 b and the inner side plate 21 c extends tangentially to the inner tubular portion 11 c. The pivotal shaft 44 of the shutter 40 is disposed in the vicinity of the inner side plate 21 c. The swing distal end of the shutter member 47 thus faces the outer side plate 21 c. The shutter member 47 opens in the rotation direction Ra of the cutting blade 14. As will be understood, when the vertical shield 45 of the shutter member 47 is opened at a certain angle, the amount of displacement of the swing distal end of the vertical shield 45 is greater than the amount of displacement of the swing proximal end. When the vertical shield 45 is opened at a certain angle, a greatly-displaced peripheral portion of the vertical shield can thus relatively largely open the passage opening 24.

The swirling velocity of grass clippings swirling within the housing 11 by the rotation of the cutting blade 14 is higher the farther the distance from the shaft center SC.

As is apparent from the above, when the passage opening 24 of the grass discharge passage 21 extending tangentially to the outer tubular portion 11 b is opened to some degree (more than 0% and less than 100% opening) with the vertical shield 45 in the intermediate mode, grass clippings swirling at a high velocity through the periphery of the housing 11 easily flow from the passage opening 24 into the grass discharge passage 21. This results in an increased efficiency in the reception of grass clippings in the intermediate mode.

FIG. 13 is a view of the lawn mower 10 with the shutter 40 in a full-close position, taken from the side of the receptacle mounted portion 22.

FIG. 14 is a view of the lawn mower 10 with the shutter 40 in a half-open position, taken from the side of the receptacle mounted portion 22.

FIG. 15 is a view of the lawn mower 10 with the shutter 40 in a full-open position, taken from the side of the receptacle mounted portion 22.

As illustrated in FIGS. 10-15, during pivotal movement of the shutter 40 between the full-close position (FIGS. 10 and 13) and the full-open position (FIGS. 12 and 15), the shutter never enters or projects into the interior of the housing 11.

Now a lawn mower according to a second embodiment of the present invention will be described with reference to FIGS. 16 to 22. Components identical to those in the first embodiment shown in FIGS. 1 to 15 are assigned the same reference numerals and will not be described.

As shown in FIGS. 16, 17 and 18, a lawn mower 100 modified according to the second embodiment is characterized in that an openable and closable lid 101 is provided at an outlet of a grass discharge passage 21, a member for opening and blocking the grass discharge passage 21 is a plug member 180 (plug) which is removable out of or insertable into the grass discharge passage 21, and a guide 170 is provided at the scroll portion 11 d.

The lawn mower 100 of the second embodiment has, as shown in FIG. 18, in order to efficiently perform bagging-mode operations, the scroll portion 11 d provided within the housing 11 for allowing grass clippings to swirl within the housing 11 while directing them to the grass discharge passage 21, and has, in order to efficiently perform mulching-mode operations, the guide 170 placed along the scroll portion 11 d, beneath a top plate 11 a of the housing 11, and a rear guide end 171 of the guide 170 opposed to a passage opening 24. The configurations of the components will be described in detail below.

The plug member 180 extends toward the rear guide end 171 of the guide 170 within the housing 11. More specifically, the plug member 180 inserted from the outlet (right side in the figure) of the grass discharge passage 21 protrudes from the passage opening 24 into the scroll portion 11 d, and a distal end 181 thereof extends in a curve along the scroll portion 11 d to the vicinity of the rear guide end 171 and is opposed to the rear guide end 171.

FIG. 19 illustrates that the grass discharge passage 21 extends rearward and upward from the housing 11 in the location of the scroll portion 11 d and a receptacle mounted portion 22 is provided at the outlet of the grass discharge passage 21. This figure also illustrates that the guide 170 is provided in the scroll portion 11 d below the top plate 11 a with a certain clearance, and the rear guide end 171 of the guide 170 is generally oriented toward the bottom of the passage opening 24, that is, a proximal end 21 d of a bottom plate 21 b. Reference sign Li is an orientation line in which the rear guide end 71 is directed toward the bottom of the passage opening 24. As shown in FIG. 20, the guide 170 is secured to the housing 11 with a plurality of bolts 175.

The plug member 180 is characterized in that a lower end 182 thereof is placed at a height substantially identical to that of the rear guide end 171, that is, in the orientation line Li. The lid 101 is closed after a grass receptacle 23 shown in imaginary lines is removed and the plug member 180 is inserted into the grass discharge passage 21. Closing the outlet of the grass discharge passage 21 can prevent the dislocation of the plug member 180.

Now, the configuration of the housing 11 and the scroll portion 11 d will be described with reference to FIGS. 18 and 19.

The scroll portion 11 d according to the second embodiment is a space enclosed by the top plate 11 a, an outer tubular portion 11 b, and a scroll-shaped inner wall 11 e formed radially outward of an inner tubular portion 11 c, and the scroll portion 11 d is connected to the passage opening 24 facing the housing 11 of the grass discharge passage 21.

The housing 11 has the scroll portion 11 d in a scroll shape connected to the passage opening 24 of the grass discharge passage 21 extending rearward and upward. The top plate 11 a is thus formed higher in level in a spiraling direction of the scroll portion 11 d (in the direction of hollow arrows Rc in FIG. 18), that is, formed deeper rearward of the plane of the paper of FIG. 18. In other words, as shown in FIG. 18, the height of the top plate 11 a of the scroll portion 11 d is smallest at a scroll proximal end portion 11 f, becomes progressively larger in the direction of the hollow arrows Rc, and is largest at a portion connected to the passage opening 24.

In this embodiment, a portion extending from the scroll proximal end portion 11 f in the direction of the hollow arrows Rc to be connected to the passage opening 24 is referred to as a “portion with the scroll portion.” A portion extending from the portion connected to the passage opening 24 in the direction of the hollow arrows Rc to the scroll proximal end portion 11 f is a “portion 11 g without the scroll portion 11 d.”

As shown in FIG. 21, the plug member 180 is integrally formed with a bottom plate 183, a side plate 184 extending upward from one side of the bottom plate 183 and a tab 185 extending upward from a central portion of the bottom plate 183.

Now, the operation of the second embodiment of the above structure will be described with reference to FIGS. 18, 19 and 22.

As shown in FIGS. 18 and 19, the lawn mower 100 of the second embodiment has the guide 170 placed along the scroll portion 11 d for allowing grass clippings to swirl within the bagging-mode housing 11 while directing them toward the grass discharge passage 21. The guide 170 is provided beneath the top plate 11 a of the housing 11, and the rear guide end 171 of the guide 170 is opposed to the passage opening 24, so that the direction Rc (the direction of the hollow arrows Rc) of an air flow that swirls the grass clippings within the housing, that is, a swirling flow, can be gradually changed and guided toward the passage opening 24 with the guide 170.

Furthermore, since the guide 170 placed along the scroll 11 d is provided beneath the top plate 11 a of the bagging-mode housing 11, the cross-sectional area of the housing 11 can be gradually changed between the portion with the scroll portion 11 d and the portion 11 g without the scroll portion 11 d. The gradual change of the cross-sectional area results in a gradual change of the flow velocity of the swirling flow between the portion with the scroll portion 11 d and the portion 11 g without the scroll portion 11 d.

Thus in the mulching mode in which the grass discharge passage 21 is closed or blocked off, a swirling flow guided by the guide 170 smoothly continues swirling within the housing 11. Grass clippings therefore hardly accumulate within the housing 11. The absence of accumulation of grass clippings allows continuous grass cutting operations. As a result, the operating efficiency in the mulching-mode is increased. Further, grass clippings can be evenly discharged downward from the housing 11. The return amount of the grass clippings returned from the housing 11 to the lawn is thus uniform, improving the finished quality of grass cutting.

In the bagging mode with the grass discharge passage 21 opened, a swirling flow (carrying flow) guided by the guide 170 flows from the passage opening 24 into the grass discharge passage 21 to discharge grass clippings into the grass receptacle 23 as shown in FIG. 22. The operating efficiency in the bagging mode can be secured.

In this manner, the operating efficiency in the mulching mode can be improved with the operating efficiency in the bagging mode secured, thereby improving the finished quality of grass cutting.

Further, as shown in FIGS. 18 and 19, the rear guide end 171 of the guide 170 is generally oriented toward the bottom of the passage opening 24, that is, the proximal end 21 d of the bottom plate 21 b, so that the flow direction Rc of the swirling flow can be gradually changed and guided below the passage opening 24. The cross-sectional area of the housing 11 can thus be more gradually changed between the portion with the scroll portion 11 d and the portion 11 g without the scroll portion 11 d. The more gradual change in the cross-sectional area results in a more gradual change in the flow velocity of the swirling flow between the portion with the scroll portion 11 d and the portion 11 g without the scroll portion 11 d.

As a result, in the mulching mode, a swirling flow guided by the guide 170 more smoothly continues swirling within the housing 11. Local accumulation of grass clippings within the housing 11 can thus be further prevented. More continuous grass cutting operations can thus be performed, further increasing the operating efficiency in the mulching mode. Also the return amount of grass clippings returned from the housing 11 to the lawn can be more uniform, further improving the finished quality of grass cutting.

Furthermore, the fact that a member for opening and closing the grass discharge passage 21 is constituted by the plug member 180 to be removed out of or inserted into the grass discharge passage 21 and that the plug member 180 extends toward the rear guide end 171 of the guide 170 within the housing 11 allows the bagging-mode housing 11 to be switched between the bagging mode and the mulching mode only by removing or inserting the plug member 180 out of or into the grass discharge passage 21. The mode switching operation is easy and allows short-time switching.

The lower end 182 of the plug member 180 extended toward the rear guide end 171 of the guide 170 is placed at a height substantially identical to that of the rear guide end 171, so that a swirling flow guided by the guide 170 passes below the plug member 180 in the mulching mode with the grass discharge passage 21 blocked by the plug member 180. In this manner, the swirling flow guided by the guide 170 can be further gradually changed and guided toward the portion 11 g without the scroll portion 11 d by the lower end 182 of the plug member 180.

The cross-sectional area of the housing 11 can thus be more gradually changed between the portion with the scroll portion 11 d and the portion 11 g without the scroll portion 11 d. The more gradual change in cross-sectional area results in a more gradual change in the flow velocity of a swirling flow between the portion with the scroll portion 11 d and the portion 11 g without the scroll portion 11 d. As a result, in the mulching mode, the swirling flow guided by the guide 170 more smoothly continues swirling within the housing 11. Grass clippings can thus be further prevented from locally accumulating within the housing 11.

In the present invention, the power source is not limited to the engine 11 and may be an electric motor, for example.

The grass receptacle 23 is not limited to a grass bag and may be a box, for example.

The vertical shield 45 and the horizontal shield 46 of the shutter member 47 may have any shape, size and material composition as long as the shutter member 47 is configured to be able to control the degree of opening of the passage opening 24.

The shutter member 47 may have the swing proximal end of the vertical shield 45 attached to the pivotal shaft 44 in any manner, including the configuration in which only the swing proximal end of the vertical shield 45 is attached to the pivotal shaft 44 or only the swing proximal end of the horizontal shield 46 is attached to the pivotal shaft 44, for example.

The guide 71 or 170 may have any shape, size and material composition.

The rear guide end 71 may have the shape and size of the depressions 71 a and the projections 71 b configured in any size an shape as long as they are in a wave shape.

The present disclosure relates to the subject matters of Japanese Patent Application No. 2002-087057, filed Mar. 25, 2002, and Japanese Patent Application No. 2002-325846, filed Nov. 8, 2002, the disclosures of which are expressly incorporated herein by reference in their entireties. 

1. A lawn mower comprising: a power source for rotatably driving an output shaft; a housing having an interior space having a generally spiral-shaped portion; a cutting blade disposed in the interior space of the housing and connected to the output shaft for rotation therewith to cut grass and coacting with the spiral-shaped portion of the interior space to generate a swirling air flow that causes the cut grass to swirl within the interior space; a grass discharge passage having an inlet end portion that opens into the interior space of the housing for receiving grass cut by the cutting blade and swirling within the interior space of the housing and a discharge end portion for discharging the cut grass; a grass receptacle detachably attached to the discharge end portion of the discharge passage; and a pivotal shutter disposed at the inlet end portion of the grass discharge passage and pivotal about a generally vertical axis for opening and closing the grass discharge passage, the pivotal shutter being pivotable between at least a first fully-closed position in which the pivotal shutter fully closes the grass discharge passage to permit the lawn mower to undergo a mulching operation for cutting grass cut by the cutting blade more finely within the housing and discharging the cut grass downward of the housing, and a second fully-opened position in which the pivotal shutter projects into and fully opens the grass discharge passage to permit the lawn mower to undergo a bagging operation for receiving in the grass receptacle grass cut by the cutting blade; wherein the pivotal shutter does not project into the interior space of the housing during pivotal movement thereof between the first and second positions, and wherein the grass receptacle is detachable from and attachable to the discharge end portion of the grass discharge passage independently of pivotal movement of the pivotal shutter between the first position and the second position.
 2. A lawn mower according to claim 1; wherein the pivotal shutter comprises a pivotal shaft and a unitary shutter member mounted on the pivotal shaft to undergo pivotal movement therewith for opening and closing the grass discharge passage.
 3. A lawn mower according to claim 2; wherein the unitary shutter member comprises a vertical shield mounted on the pivotal shaft for undergoing pivotal movement therewith to open and close the grass discharge passage, and a horizontal shield extending transversely from a bottom portion of the vertical shield for closing a lower portion of an inlet of the grass discharge passage.
 4. A lawn mower according to claim 2; further comprising a manually movable control member connected to the pivotal shaft for pivoting the pivotal shaft in response to manual movement of the control member to effect pivotal movement of the shutter member to at least first and second positions for opening and closing the grass discharge passage.
 5. A lawn mower according to claim 4; further comprising a control guide disposed above the grass discharge passage for guiding movement of the control member, the control guide having two laterally-spaced positioning notches receptive of the control member and an elongated hole interconnecting the two positioning notches, wherein when the control member is received in one of the two positioning notches, the shutter member is in the first position and fully closes the grass discharge passage, and when the control member is received in the other positioning notch, the shutter member is in the second position and fully opens the grass discharge passage.
 6. A lawn mower according to claim 5; wherein the control guide has three or more spaced-apart positioning notches receptive of the control member and the elongated hole interconnects all of the positioning notches, two of the three or more positioning notches being located at opposite ends of the longitudinal hole, and the remainder of the three or more positioning notches being disposed between said two positioning notches.
 7. A lawn mower according to claim 2; wherein the pivotal shutter is pivotable between the first position in which the shutter member fully closes the grass discharge passage, the second position in which the shutter member projects into and fully opens the grass discharge passage, and a third position in which the shutter member projects into and partly opens the grass discharge passage.
 8. A lawn mower according to claim 1; further including a guide disposed in the housing and extending circumferentially partway around the interior of the housing for guiding cut grass toward the grass discharge passage.
 9. A lawn mower according to claim 8; wherein the guide has a rear end that terminates at the inlet end portion of the grass discharge passage.
 10. A lawn mower according to claim 1; wherein the lawn mower has only a single cutting blade.
 11. A lawn mower, comprising: a power source for rotatably driving an output shaft; a housing having an interior space having a generally spiral-shaped portion; a cutting blade disposed in the interior space of the housing and connected to the output shaft for rotation therewith to cut grass and coacting with the spiral-shaped portion of the interior space to generate a swirling air flow that causes the cut grass to swirl within the interior space; a grass discharge passage having an inlet end portion that opens into the interior space of the housing for introducing into the grass discharge passage grass cut by the cutting blade and swirling within the interior space of the housing and a discharge end portion for discharging cut grass from the grass discharge passage; and a pivotal shutter disposed at the inlet end portion of the grass discharge passage and pivotal about a generally vertical axis between a first fully-closed position in which the pivotal shutter closes the grass discharge passage and a second fully-opened position in which the pivotal shutter projects into and opens the grass discharge passage, wherein the pivotal shutter does not project into the interior space of the housing during pivotal movement thereof between the first and second positions.
 12. A lawn mower according to claim 11; wherein the pivotal shutter comprises a pivotal shaft and a unitary shutter member mounted on the pivotal shaft to undergo pivotal movement therewith for opening and closing the grass discharge passage.
 13. A lawn mower according to claim 12; wherein the unitary shutter member comprises a vertical shield mounted on the pivotal shaft for undergoing pivotal movement therewith to open and close the grass discharge passage, and a horizontal shield extending transversely from a bottom portion of the vertical shield for closing a lower portion of an inlet of the grass discharge passage.
 14. A lawn mower according to claim 12; further comprising a manually movable control member connected to the pivotal shaft for pivoting the pivotal shaft in response to manual movement of the control member to effect pivotal movement of the shutter member for opening and closing the grass discharge passage.
 15. A lawn mower according to claim 14; further comprising a control guide disposed above the grass discharge passage for guiding movement of the control member, the control guide having two laterally-spaced positioning notches receptive of the control member and an elongated hole interconnecting the two positioning notches, wherein when the control member is received in one of the two positioning notches, the shutter member is in the first position and fully closes the grass discharge passage, and when the control member is received in the other positioning notch, the shutter member is in the second position and fully opens the grass discharge passage.
 16. A lawn mower according to claim 15; wherein the control guide has three or more spaced-apart positioning notches receptive of the control member and the elongated hole interconnects all of the positioning notches, two of the three or more positioning notches being located at opposite ends of the longitudinal hole, and the remainder of the three or more positioning notches being disposed between said two positioning notches.
 17. A lawn mower according to claim 12; wherein the pivotal shutter is pivotable between the first position in which the shutter member fully closes the grass discharge passage, the second position in which the shutter member projects into and fully opens the grass discharge passage, and a third position in which the shutter member projects into and partly opens the grass discharge passage.
 18. A lawn mower according to claim 11; further including a grass receptacle removably attached to the discharge end portion of the grass discharge passage; wherein when the pivotal shutter is in the first position, the grass discharge passage is fully closed and the lawn mower is placed in a mulching mode and discharges the cut grass downwardly of the housing; and wherein when the pivotal shutter is in the second position, the grass discharge passage is fully opened and the lawn mower is placed in a bagging mode and discharges the cut grass through the grass discharge passage into the grass receptacle.
 19. A lawn mower according to claim 11; further including a guide disposed in the housing and extending circumferentially partway around the interior of the housing for guiding cut grass toward the grass discharge passage.
 20. A lawn mower according to claim 19; wherein the guide has a rear end that terminates at the inlet end portion of the grass discharge passage.
 21. A lawn mower according to claim 11; wherein the lawn mower has only a single cutting blade. 